According to a conventional technique, atomizing a fluid material, is atomized by jetting compressed air jetted from a nozzle, dispersed in the air and then jetted to a preferred surface. The form for supplying the jetted air flow in this kind of atomizing device varies and depends on respective fluid material.
For example, in a general arc fusing device, a linear or band-shaped metal material is fused by arc heat, atomized by a compressed air for atomizing and jetted, while being cooled, to a given object, thereby an atomized coating is formed on the object. According to this kind of arc fusing device, there are two known systems to supply the compressed air: an external enclosing system to form a main air jet curtain at an external side of an arc area and a penetrating system to jet the main air jet curtain toward the arc area from its central, rear pan.
In the external enclosing system, the main air jet curtain is jetted in a conical form from an annular nozzle, thereby forming a low pressure zone inside the conical air flow, and a metal material is supplied in the low pressure zone. Then, arc discharge is carried out, and the metal molten material is atomized on contact with the conical air flow. A fusing device according to this technique is known in Japanese Laid-open Patent Publication No. 61-167472. Further, according to Japanese Laid-open Patent Publication No. 56-10103, in order to supply the metal molten droplets exactly into the main air jet curtain, a second nozzle is disposed behind a center of the arc area, and a supplementary air jet is jetted toward the center of the arc area from the second nozzle.
In this type of fusing device, the main air jet curtain of the conical form is formed outside the metal material and the arc area. For this reason, the foregoing fusing device becomes larger than that of the penetrating system, and its construction also becomes more complicated. In particular, when using the band-shaped metal material, the caliber of the annular nozzle must be larger. Otherwise, the arc area cannot be covered by the main air jet curtain.
Further, in the fusing device having the supplementary nozzle disposed behind the center of the arc area, its internal construction becomes more complicated. In this case, it is required to connect two separate air hoses having a different air pressure to the main nozzle and the supplementary nozzle, respectively. However, good operability was hindered.
The penetrating system is provided with the main nozzle for jetting the main air jet behind the center of the arc area, whereby the metal molten droplets are atomized by the main air jet jetted linearly from the main nozzle. This kind of device is disclosed for example in Japanese Laid-open Patent Publication No. 61-181560.
Further, according to Japanese Laid-open Patent Publication No. 60-18463, a pair of supplementary nozzles are disposed outside the arc area independently of the main nozzle, thereby supplementary air is jetted toward a pointed end of the metal material from the pair of supplementary nozzles. Thus, the metal molten droplets are atomized by joint cooperation of the supplementary air and the main air jet.
In the penetrating system, atomization is carried out by jetting the main air jet directly to the arc area. For this reason, the arc area of the metal material is cooled by the main air jet, thereby easily causing abnormally high temperature due to a pinch effect. As a result, oxygen in the main air jet becomes a high temperature and high density ozone, thereby the metal molten is forced to be oxidized severely or to be fused explosively. Thus, the metal molten droplets not yet atomized are jetted to the object, so that coating becomes irregular. To remove this disadvantage, the penetrating system also uses the supplementary nozzles, but the structure is apt to be complicated.
As discussed above, both systems have some merits and demerits in view of construction and fusion performance. Now, it is necessary to make further improvements.
In view of the above, this invention has been accomplished. It is therefore a general object of this invention to provide an atomization method and its atomizing device, wherein the construction of the fusing device is simplified, namely more compact and lighter by improving the supply form of the compressed air for atomizing, and the fusing by arc heat can be carried out stably.
It is another object of this invention to provide an atomization method and its atomizing device which enables supplying the compressed air for atomizing, suitable for a band-shaped metal material.
Referring to a second problem of the foregoing fusing device or other type of it, the disadvantage is that its fusing pattern is small and the distribution of minute molten droplets jetted on the object become irregular.
According to a conventional device as shown in FIG. 26, a fusing pattern P2 forms a nearly circular form, so that only a smaller fusing area is available. When increasing the air quantity to be jetted from a nozzle, it is possible to enlarge the fusing area to some extent. But the arc area of the material is cooled excessively and is susceptible to a pinch phenomenon, thereby it becomes difficult to carry out the arc fusing stably. Further, since either the arc fusing system or a gas fusing system forms a strongly reversing air flow upon the surface of the object to be coated by atomization, the metal molten droplets are spattered without adhering to the object, so that its loss is increased rapidly.
Preferably, a distance between the fusing device and the object is about 20 cm, but it is possible to enlarge the fusing area to some extent by increasing this distance. Yet, in this case, the adhesive force of the atomized, molten droplets to the surface of the object is decreased, and the anti-stripping strength of the coating is also decreased.
According to the conventional device as shown in FIG. 26, the thickness of a membrane of the circular fusing pattern P2 is considerably thicker at the central part of it, and becomes so thin at its peripheral side. For this reason, the thickness of the membrane is irregular in a superficial direction, so that a uniform coating cannot be obtained. Further, since the molten droplets are concentratedly jetted to a central part of the object, heat is accumulated in that part, so that the coating is stripped from the object due to a heat expansion difference between the central part and the peripheral part.
As discussed above, an operational efficiency of the present device depends on the size of the fusing pattern area. It takes of course a long time to form a coating having a certain thickness on a given area. Prior to fusing, the object is treated with a blast treatment, thereby its surface is activated, but susceptible to oxidation. Accordingly, the fusing operation must be finished within 2 to 4 hours after the blast treatment. When the area of the object reaches a certain value beyond the capacity of the fusing device, it is no more possible to make coating within the foregoing hours. In that case, it is required to carry out an additional operation including an activating treatment by use of a solvent.
It is another object of this invention to provide a high efficiency fusing device which enables enlargement of the fusing area by a few times and makes the distribution of the membrane a uniform thickness by improving the supply form of the compressed air for atomizing.
An air atomizing spray gun for painting as a typical atomizer is used widely. By disposing an air cap on a nozzle end, a paint and air are mixed with each other at the nozzle opening, thereby atomizing the paint. Further, as necessity arises, any additional nozzle may be disposed to promote atomization, adjust a coating pattern or prevent spattering of the paint.
Apart from the foregoing air atomizing system, the spray gun has a popular airless system for causing a friction with an ambient air by jetting high-speedily a highly pressurized painting liquid from a small nozzle tip. In either system, such a conventional atomizer for painting needs a nozzle for atomizing the paint liquid. For this reason, clogging at the nozzle is always a problem. Every time spraying is carried out, a cumbersome cleaning work is required. Further, most failures such as malfunction of the atomizing device or a bad coating pattern derive from the nozzle. Therefore, it is very cumbersome to keep good maintenance of the nozzle.
Further, such a conventional atomizer has the problem that brings a large quantity of ineffective mists when spraying. Because the paint is atomized at the nozzle tip by a mutually intersecting collision of a plurality of air jets, such unnecessary mists arise. If their quantity is so large, the paint liquid is consumed wastefully. In addition, the working environment is polluted by such paint liquid or solvents.
In either Japanese Laid-open Patent Publication No. 59-206066 or Japanese Laid-open Utility Model Publication No. 57-55560 relating to the airless type spray gun for removing ineffective mists, there is disclosed the technique that an annular air nozzle is disposed around a nozzle for jetting paint, and then the atomizing area of the paint is enclosed by the air curtain jetted from the air nozzle. However, when spraying the paint liquid, part of the air curtain simultaneously covers a wet sprayed surface, thereby it is disturbed by the air curtain, and the quality of coating is deteriorated. Further, the disadvantage is that the air nozzle for the air curtain must separately be disposed in addition to the atomizing means.
Further, since the conventional device needs to form atomizing means such as the nozzle accurately and make an accurate position relationship between the atomizing means and the air nozzle, the disadvantage is that the cost for manufacturing the atomizer becomes expensive. According to the airless type spray gun, since the paint liquid is pressurized to high pressure of 100 to 200 Kg/cm.sup.2, the supply system for the paint is very expensive.
It is another object of this invention to provide an atomization method and its atomizing device, which enables solving the clogging problem of the nozzle and carry out an easy operation.
It is another object of this invention to provide atomization method and its atomizing device, which enables preventing occurrence of the ineffective mists, eliminate a wasteful consumption of the paint and wipe away any contamination of the working environment.
After all, the ultimate object of this invention is to atomize the fluid materials such as the metal molten droplets, paint or the like exactly and stably by a novel atomizing means, thereby enables realizing a high fidelity of the atomizing device and reducing the manufacturing cost.